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I'm sure that this isn't a squat lobster (these have four pairs of legs, plus a couple of tiny vestigial ones at the rear), and I'd agree with The Woodman that a small Maja squinado is the most likely option. The lack of orange is a bit strange, but I guess it's just a badly worn specimen, which would explain why a lot of the spines are missing. Shape & structure wise, there are some similar examples here Spiny Spider Crabs, Maja squinado